Private automatic exchange



w. A. cHAPlN PRIVATE AUTOMATIC EXCHANGE Filed octj24. 1921 3 Sheets-,Sham 2 www Y IW. CHAPIN PRIVATE AUTOMATIC EXCHANGE Filed om. 24. 1921 s smms-smm Inuannr Mmmm lEh-alpm 'lil Patented Nov.. i8, i924..

/VTLLIAM A. CHAPIN, OF CHICAGO, ILLINOIS, ASSGNOR TO riti.

AUTOMATIC ELECTRIC *arr COllllAlVY,l 0F CHCAGO, TLLNOIS, A. CORPORATTON OF TLLINO'IS.

PRIVATE AUTOMATIC EXCHANGE.

Application led October 24, 1921.

To all whom. t may concern.'

Beit known that l, WILLIAM: A. C'HAPIN, a citizen of the United States of America, and a resident of Chicago, Cook County, and State of Illinois, have invented certain new and useful Improvements in Private Automatic Exchanges, of which the following is specification.

The present invention relates to private automatic exchanges in general, but is concerned more particularly with exchanges of this character which areprovided with code signalling arrangements, whereby certain persons may be reached when they are absent from their offices on business in other departments; the yobject briefly stated is the provision of new and improved circuit arrangements tending to make a Vcode signalling system of this sort more flexible in operation and more desirable from the standpoint of the user.

In order to explain the object above set forth a little more fully it may be said that it has been common practice heretofore to provide a single code switch which has two sets of terminals. The so called calling` set of these terminals is seized by an automatic switch under the control of a calling subscribers calling device when a certain number is called. After this set of terminals is seized, one or two additional digits are dialled in order to setup the code switch and cause it to send out the desired code. This code, it will be understood, is sent out over a circuit onto which there may be multipled as many signalling` devices as desired. l/Vhen a subscriber hears his code being sent out he responds by dialling a certain other number with the result that an automatic switch connects with the code switch at the other o1' so called answering set of terminals. The two subscribers then proceed to converse with each other as desired. As long as they converse, however, the code switch remains tied up and cannot be used by any one else. According to the present invention, however, a plurality of repeaters are provided each having a set of calling and a set of answering terminals and each being normally connected to the code switch. Now when a subscriber who desires to send out the code of another subscriber dials a certain digit or combination of digits, one of these repeaters is seized at its calling set of terminals and in response to the calling Serial No. 509,974.

of the two following digits the code `switch is set up with the result that the desired code is sent out intermittently in the usual manner. New as soon as the subscriber who hears his cod-e being sent out respondsby dialling a certain digit or combination of digits this same repeaterV is seized at its answering terminals with the result that it is entirely disconnected from the code switch and the two subscribers are free to converse with each other through the said repeater, leaving the code switch freeto be used by any one else who desires to do so.

It happens many times that an establishment is physically or otherwise divided into two or more parts, for example, an'

establishment served by one private automatic exchange, or P. A. Xi. as it is commonly abbreviated, may comprise two buildings and in such cases it often happens that there are certain persons who have occasion to be away from their desks but who do not have any occasion to leave the building in which they are employed, while certain other persons may have business in either of the two buildings. rlhis makes it unnecessary, when sending out a code of signals for a person who is absent from .his department but who has no occasion to leave the particular building in which .he is employed, to operate the signals in both buildings and accordingly it has been common practice under such circumstances to place the signals in one building on one circuit andthe signals in the other building on another circuit, the signals in one building being operated by a code lswitch which has its terminals multipled in certain bank contacts, and the signals on the other circuit being operated by a second code switch which'has its calling and answering terminals multiplied in other bank contacts; and for operating the two sets of signals simultaneously Ya third code switch is `provided which has its calling and answering terminals multiplied in still other bank contacts. This arrangement, while obviously more or less satisfactory from the stand point of the subscriber, is wasteful in equipment and is further objectionable because of the fact that a separate answering number must be assigned for each of the three switches. In the present case, however,this difficulty is overcome by arranging the signals so that they are all normally connected onto one circuit and are consequently operated simultaneously. In order to discriminate bev tween one set or the other, separate groups multipled into another selector level.

Y installations, however, where there are two or-more sets of signals to be operated sepcrimination whatsoever of repeaters are provided from which the common code switch may be controlled. Vhen the code Switch is being operated from a repeater of one set, all the signals are operated simultaneously. lhen the said code switch is-being operated from a repeater of a second group, a ground potential is placed upon a conductor individual to this group which operates a relay in the code switch to disconnect one set of signals; and when the code switch is being operated from a repeater inthe third group, a ground potential is placed upon a conductor individual to that group which operates a relay in the code yswitch to disconnect the other set of signals.

In a simple system inwhich there is only oneset of signals to be operated, the repeaters are all in one group and consequently all the calling terminals of the various repeaters may be multipled into one selector level and all the answering terminals may be In arately Vor collectively, it is necessary to provide a separate selector level for the calling terminals of each group of repeaters. In all cases, however, the answering terminals of all the repeaters in the various groups are multipled into one common selector levelas it is not necessary to use any disin answering a code.

There are various other features of the invention which will not be pointedrout specifically at this time but which will be explained in detail in the course of the specification.

Referring now to the drawings comprising Figs. 1, 2, and 8, when they are arranged in order with the corresponding lines at the ends thereof in alignment, they represent by means of the usual circuit diagrams a sutlicient amount of the apparatus in a systern embodying the principles of the invention to enable the invention to be thoroughly understood. In Fig. 1, there is shown two subscribers lines, together with their associated substations and individual line switches, and also two of the selector switches to which the individual line switches have access.

Fig. y2 shows one of the repeaters which is normally connected with the common code switch.

In Fig. 3, there is shown the code switch together with two signal circuits and their .signals S--S3, inclusive.

The line switches C and C are mechanically of the well known rotary type in which the wipers have no normal position and move in a forward direction only. The impulse switch I, Fig. 3, which is associated with the code switch F, is mechanically similar to the line switches C and C but its circuit differs as shown.

The selectors D and D and also the code switch F are automatic switches of the well known vertical and rotary type and accordingly have their bank contacts arranged in horizontal rows or levels. The circuits of the selectors D and D are identical with each other and are of a well known type, but the circuits of the code switch F differ radically from the circuits of the selectors as will be pointed out fully hereinafter.

The repeater E, Fig. 2, as before intimated, is one of the repeaters which is used to enable the common code switch to be disconnected and used over again immediately after a wanted subscriber has answered his code by dialling the answering number. The circuits of this repeater are shown in full and will be described hereinafter.

The apparatus, having been described more or less in general, will now be described in connection with a detailed description of its operation. For this purpose it will be assumed that the subscriber at substation A has called a certain other subscriber by way of the telephone at the latters desk and having received no response has released the connection and decided to try to reach the desired subscriber by sending out his code. It will be assumed further that the code of the man wanted is 45 which comprises four rings or buzzes, pause, and tive rings or buzzes. It will be assumed also that this man is one whose business does not take him out of the building in which he works and in which the signals S and S are located.

When the receiver is removed at substation A, a circuit is closed over line conductors 11 and 12 for the line relay 15 of line switch C. Line relay 15, upon energizing, places ground upon private normal conductor 13 at armature 21, thereby causing the line of sub-station A to test busy to the automatic switches which have access to it, and also closing a circuit for switching relay 14 and stepping magnet 16 in series; and at armature 2O connects the test wiper 23 to a point between switching relay 14 and stepping magnet 16. The line switch C is now operated in the usual and well known Inanner to pick out an idle trunk line. Assuming that the trunk line extending to the selector D is the first one found to be idle, when the wipers 22-24, inclusive, arrive upon the set of bank contacts in which the trunk line comprising conductors 25u27, inclusivel` terminates, switching relay 14 energizes in series with stepping magnet 16, not having energized before on account of being short circuited by the ground potential which is present upon the test contacts of busy trunk lines. Stepping magnet 16, however, does not energize in series with switching relay 14 onl account of its relatively low resistance and correspondingly stiff adjustment. Upon energizing, switching relay 14 disconnects test wiper 23 from` the point between its own winding and that of stepping magnet 16 and connects it to the grounded private normal conductor 13 at armature 18, thereby making the seized trunk busy immediately by placing a ground potential upon release trunk conductor 26. As a further result of the energization of switching relay 14, it disconnects th-e line conductors 11 and 12 from the winding of line relay and ground respectively, and extends them by way of armatures 17 and' 19 and their working contacts, wipers 22 and 24, conductors 25 and 27, and armatures 56 and 59 and their resting contacts, to the upper and lower windings of line relay of selector l). Line relay 35 now energizes over the calling subscribers loop and at its armature 50 closes a circuit for release relay 36. Release relay 36, upon energizing, opens a point in the circuit of release magnet and prepares a circuit for vertical magnet 41 at armature 52, and at armature 51 places ground upon release trunk conductor 26, thereby establishing a holding circuit for switching relay 14 of the line switch C before the slow acting line relay 15 has had time to deenergize The calling subscriber may now manipulate his calling device inv accordance with the digit which it is necessary to call preparatory t0 sending out a code upon the desired set of signals, thereby producing a corresponding number of interruptions in the circuit of line relay 35. Each time line relay v35 deenerg'izes in response to one of these interruptions, it completes a circuit for vertical magnet 41 as follows: From ground by way of the resting contact of armature 58 and said armature, armature 50- and its resting contact, armature 52 and its working contact, series relay 37, and vertical magnet 41 to battery. By the operation of vertical magnet 41, the shaft and wipers of the selector D are raised step by step until the latter come to rest opposite the desired level of bank contacts. Relay 37 is energized in series with vertical magnet 41 and being slow acting retains its armature attracted throughout the vertical movement. Off normal springs 44, upon closing as soon as the switch shaft is raised from its normal position, completes the following circuit for stepping relay 38: from ground by way of release trunk conductor 26, armature 53 and its working contact, interrupter contacts of rotary magnet 42, off normal contacts 44, and stepping relay 38 to battery. Stepping relay 3S, upon energizing, closes a locking circuit for itself at armature 54, and at armature 55 prepares a circuit for rotary magnet 42. At the end of the vertical movement, relay 37, upon deenergizing, completes the circuit of rotary magnet 42 at armature 53. Rotary magnet 42, upon energizing, advances the switch wipers -62, inclusive, into engagement with the first set of contac-ts in the level opposite which they are raised, and at interrupter contacts 45 opens the circuit of .stepping relay 38. Stepping relay 38, upon deenergizing, opens the circuit of rotary magnet 42 at armature 55, whereupon the said rotary magnet deenergizes and closes its interrupter contact` again. lf the trunk line terminating in the first set of contacts is busy stepping relay 38 is energized again by way of test wiper 61 and armature 57 and its resting contact with the result that the wipers are rotated into engagement with the next set of contacts. rllhis operation continues until an idle trunk line is-reached which we shall assume, is the trunk line comprising conductors 63-65, inclusive, and extending to the repeater E. 1When the said idle trunk is reached thereis no circuit closed for stepping relay 38 land switching relay 39, which heretofore 4has been short circuited, energizes over `the following circuit: from ground by way of release trunk conductor 26, resting contact of cam spring 46 and said spring, switching relay 39, interrupter contacts 45, o normal contacts 44, and stepping relay 38 to battery. Stepping relay 38, however, dueto its design and adjustment does not energize in series with switching relay 39. Switching relay 39, upon energizing, removes ground from the armature of line relay-35 at armature 58; opensthe test circuit and prepares the holding circuit at armature 57, thereby placing ground upon releasetrunk conductor 64 of the repeater E; and disconnects trunk conductors 25 and 27 from-the upper and lower windings of line relay' 35 and extends them by way of armatures 56 and 59 and their working contacts, wipers 6() and 62, the bank contact-s with which these wipers are in engagement, conductors 63 and 65, and armatures 81 and 82 and their resting contacts to the upper and lower windings of line relay 73 of the repeater E. Line relay 7 3, upon energizing over the calling subscribers loop, closes a'circuit for release relay '74 at armature 84. Release relay 74, upon energizing, places ground upon release trunk conductor 64 at armature 87, by way of the normally closed contacts controlled by armature 93, and its own low resistance lower winding, thereby establishing aholding circuit for the 'switching relays of the selector D and the line switch `C before the slow acting release relay 36 of the selector D has had time to deenergize. This lower winding of release relay 74 is low enough to allow the various test contacts into which release trunk conductor 64 is multipled to remain sufficiently near a ground potential to cause them to test busy. The reason for bringing the holding ground through the lower winding of release relay 74 will be explained more fully hereinafter. A branch of this holding circuit extends by way of armature 97 to relay 77 and itsresting contact, to battery by Vway of relay 78. kRelay 78, upon energizing, disconnects the release trunk conductor 57 of the answering set of terminals from conductor 112 which, together with conductors 111 and 113, is common to all the repeaters of the various groups, and connects it to relay 79 at armature 100, and at armature 101 disconnects relay 77 from conductor 112. As a further result'of the energization of release relay 74 it places ground upon conductor 112 at armature 86, by way of armature 103 and its resting contact.

In vthe 'code switch F, release relay 123, upon energizing, in response to the placing of ground. upon 'conductor 112, opens a point in the circuit of release magnet 133 at armature 147.

Since conductor 112 is common to all the repeaters, all that are idle are made busy at both their answering and calling terminals. Assuming, for the purpose of illustration, that the repeater E is one of the other repeaters, the ground potential, comingin by way vof conductor 112, extends by way of the resting contact of armature 100 and said armature to the answering release trunk conductor 67, and by the way of the resting contact of armature 101 and said armature, to battery by way of relay77. Relay 77, upon energizing, places ground upon the calling testconductor 64. This, of course, occurs only in the repeaters that are idle. j

To continue with the operation of the repeater E, as a result of the ground potential being placed upon conductor 112, a circuit is closed for relay 80 by way of armature 99 and its working contact and the resting con-tact of armature 105 and said armature. 'Relay 80, upon energizing, closes a *locking circuit for itself at armature 107, and at armature 106 places ground upon conductor 114, thereby closing` a circuit for relay 126 of the code switch F which, upon energizing, disconnects the signals S2 and S3 at armature 151.

The calling subscriber may now operate his calling device in accordance with the iirst digit 4 of the desired code, thereby producing a corresponding number of interruptionsin the circuit of line relay 73. Each time line relay 73A deenergizes in response to one of these interruptions, it completes a circuit for vertical magnet 131 of the code switch F as follows: from ground by way of armature 84 and its resting` contact, armature 88 and its working contact, armature 104 and its resting contact, conductor 113, resting contact of ofi' normal spring 135 and said spring, relay 120, and vertical magnet 131 to battery. By the operation of vertical magnet 131, the shaft and wipers of the code switch F are raised step by step until the latter come to rest opposite the desired level of bank contacts, which in this case is the fourth. rllhe low wound relay 120 is energized in series with vertical magnet 131 and being` slow acting retains its armature attracted throughout the vertical movement, thereby maintaining its own circuit and that of vertical magnet 131 intact after the off normal springs have been shifted, as they do upon the first vertical step. .at the end of the vertical movement, slow acting relay 120 deenergizes and transfers the operating circuit from the vertical to the rotary magnet.

lin the repeater ll it will be noted that each. time line relay 7 3 deenergizes it closes circuit for relay 71 as follows: from ground by way of armature 89 and its working` contact, armature and its resting contact, armature and its resting contact, and relay 71 to battery. Relay 71, however, being stitly adjusted and having a highly inductive winding, does not energize as long armature 85 is vibrating.

The calling subscriber now manipulates his calling device in accordance with the second and last digit 5 in the desired. code, thereby producing tive interruptions in the circuit of line relay 73 of the repeater E. Each time relay 73 deenergizes in response to one of these interruptions it closes a cir cuit for rotary magnet 132 of the code switch F as follows: from ground by way of armature 84 and its resting contact, and thence by way of the previously traced circuit to conductor 113, and thence by way of the normally open contacts controlled by olf normal spring 135, armature 141 and its resting contact, resting contact of armature 146 and said armature, relay 121, and rotary magnet 132 to battery. By the operation of the rotary magnet the wipers 157 and 158 are rotated into engagement with the fifth set of contacts in the fourth level. Relay 121 is energized in series with rotary magnet 132 and, being slow acting, retains its armature attracted throughout'. the rotary movement. Upon energizing, relay 121 places a shunt around the resting contact of armature 146 and said armature at armature 143, and at armature 142 closes a circuit for relay 122.

Relay 122, upon energizing, closes a locking circuit for itself at armature 145, and at armature 144 prepares a starting circuit for the interrupter relays 127 and 128. At the end of the rotary movement, relay 121 de- .energizesg ,opens its `,own circuit and that of Vrotary magnet `182 4lat-.armature y143 so that any Vfurther movement .of the subscribers .calling .device will vbe ineffective in operat- Jingrotarymagnet132; opens the initial circuit of relay 122 at armature 142, at the -same time placing vground upon starting .conductor 165 by way .of the working contact of'armature -144 land said armature. As soon asfground is lplaced upon starting conductor 165,7a circuit is closed by way oi' the resting contact of armature 152 and said armatureior relay 128. Relay 128, upon energizing, closes :a circuit for relay 127 at "larmature 153. Relay l127, upon energizing,

.opens .the circuit .of .relay 128 at armature 152. Relay 128, however, being slow acting, retainsits armature attracted .for an interval lafterwhich it falls backand opens the circuit-of .relay 127 at armature 153. Relay .127,fbeing slow acting, retains its armature attractedtorfan interval after which it falls back-and .closesthecircuitof relay 128 again. .alternate operation ,of .relays 127 and i128 `continues as .longLas there vis a ground potential upon conductor 165. Each time relay A128-energi-zes, in Iaddition to closing the circuitof relay 127, it closes the circuit ot `stepping-magnet-162 of the switch 1. Each `time .magnet 162 energizes, it attracts its armature, thereby causing it to engage anothernotchfon the associated ratchet wheel -whichdrivesthe wipers 160 and 161. Each .time `stepping magnet 162 deenergizes, the `associatedwpers 160and 161 are advanced into .eng-agement with the next set of bank contacts.

VThe `wipers 160;and 161vare shown in their normal position `andconsequently as soon as the magnet 162 has fenergized and deener- `gized once the wipers are rotated onto the `first setof contacts. As soon as this occurs `a ground potential is placed upon the pick up conductor 171 which is multipled to the ltop contact of each set of contacts in the fifth level of the code switch F. Since the Wipers157-fand .158 are not in engagement withany contactsfin .thefth level this does lnotproducefany `result at this time. As soon as stepping :magnet w162 has energized and `deenergized again, `the wipers 160 and 161 arefadvanced Vinto .engagement with the sec :ond set :of associated .bank contacts and a :ground potential .is placed .upon conductor i172 `whichLisi'iniiltipled to .the .upper contact offeachf'set inztheourthlevelgofzthe bank of the'codeswitch Since .thewiper 157 is in `enga'gement kwiththe upper Vcontact of the fitth feet lin'the fourth level, the following ciricuitfis :closed: ifrom ground way of *wiper y161, the second associated bank .contact, `conductor 5172, the upper bank contact 'ldt the tth 'set iin .fthe tourth level of the "switch iT,wiper ,157," pickup "conductor 177, @pick apli-'clay `."1? (1,:'and .resistance `129 to battery. Upon energizing, pick up relay .130

prepares a circuit for impulsing relay 12.4

`edat armature 151 of relay 126. As soon `as interrupter relay 128 deenergizes, stepping magnet 162 advances the wipers 160 and 161 into engagement with the third set of contacts and impulsing relay 124 deenergizes, thereby opening the circuit of the signals S and S. The wipers 160 and 161 continue to advance and the signals S andS continue to be operated until vthe said wipershave been advanced into engagement with .the sixth set ot contacts in their associated bank, when the `signals S and .S will have been operated four times.

As soon as the wiper 161 comes .intoen- .gagement with its sixth bank contact, the following circuit isclosed: from groundby way of wiper 161, the sixth associated bank contact, .stop conductor 176, and resistance 129 to battery. It is evident that when this circuit is closed relay 130 is short circuited. Upon deenergizing, relay 180 opens litsrpreviously closed locking circuit and disconnects impulsing relay 124 at armature 155. The next time interrupter relay 128 ener gizes, stepping relay 162 causes its armature to be attracted but impulsing relay 124 is obviously not operated. Stepping magnet 162, upon deenergizing, advances .the wiper 161 into engagement with the next set of contacts, whereupon a ground potential is placed on pick up conductor 177 and pick up relay 130 is again operated. Accordingly the next time relay 128 closes a circuit tor stepping magnet 162, a branch of this .circuit extends by way of armature 155 and its working contact to impulsing relay 124, and the said relay, upon energizing, operates the signals S and S. When `relay 128 deenergizes, the signals VS and S .are disconnected and the wipers 160l and.161 are advanced into engagement with the eighth set ot contacts, whereupon ground is placed upon stop `conductor 178. This 'stop conducto-r, is multipled to the `lower .Interrupter relay 128 continues .to :operate and the signalsS and S continue Ato beoperated in the manner V described until the wipers 160 and 161 come into engagement with the twelfth set of associated bank contacts at which time the signals S and S will have finished sending out the second digit ve in the code 45. As soon as wiper 161 arrives upon the twelfth contact the :tollowing circuit is closedrtrom ground by way of wiper 161, 'the twelfth associated bank contact, stop conductor 182, the lower contact of the itth set in the fourth level of the bank or" the switch F, wiper 158, stop conductor 176, and resistance 129 to battery.

In response to the closure or this circuit,

pick up' relay 180 deenergizes, thereby disconnecting impulsing relay 124. The wipers 160 Yand 161 continue to advance with the result that the code. 45 is sent out by the signals S and S each time the said wipers make one halt' of a revolution. It will be noted that each time relay 124 energizes to close the circuit of the signals S and S it disconnects conductor 111 from ground and connects itto battery by way of the resistance 136. There is a condenser connected in series with conductor 1 11 and accordingly a momentary charge and discharge through this condenser is eiected each time relay 124 operates. -This is done so as to apprise the calling subscriber of the fact that the desired code is being sent out.

lThe calling subscriber after listening in the receiver' to make sure that he has made no mistake in operating his calling device and that the desired code is being sent out, may replace his receiver while waiting for the rcalled man toI answer. When the receiver" is replaced at substation A, the circuit of line relay 73 of the repeater E is opened. Line relay 7 3, upon deenergizing, opens the circuit of the upper winding of release relay 74 at armature 84. Release relay 74, however, does not deenergize at this time for the reason that it is held up by the current flowing through its lower winding. As afurther result of the deenergizationv of line relay 7 8, it closes the circuitof relay 71 at armature'S. Relay 71, upon energizing, disconnects conductors ..768 andA l fromV the windings of line relay 73 and connects them to ground and to battery respectively, ring cut ofi relay 72 being in series with conductor 65. This, however, does not produce any further result at this time for the reason that there '1s no direct current circuit closed across the conductors 63 and 65, which extend back through the established connection to the bridged bell at the substation A.

When -the called man hea-rs hiscode being sent out, he responds by taking the receiver oil the nearest substation which we shall assume-is the substation A. When this ocmanner to extend the connection to an idle selector, which we shall assume is the seM lector D, whereupon the line and release relays of the said selector energize and prepare the switch for operation in the usual manner.

The man who has been signalled, may now operate the calling device at the substation A in accordance with the digit which it is necessary to call in order to answer a code, thereby producing a corresponding number ot interruptions in the circuit of the line relativ el the selector D. The selector D now raises its wipers to the desired level and rotates them in the usual manner to i'ind the terminals ot the repeater E. The said sev lector will not stop upon a set of bank contacts in which any of the other answering terminals are multipled for the reason that they are all made busy at this time. llllhen the wip-ers of the selector D arrive upon the set oic bank contacts in which the conduetors (i6-66, inclusive, terminate, it cuts through in the usual manner, thereby placing ground upon conductor 67 and extendthe connection through to the upper and lower windings of back bridge relay 76. In response to the placing of ground upon conductor 67.` a circuitl is closed for relay 7 9 of the repeater E by way of armature and its working contact. Relay 7 9, upon energizing, disconnects ground -from conductor 1 2 and closes a locking circuit for itselt at mature 10?). The closing ot this locking ci it establishes vthe usual holding circuit for the selector D and the line switch C. its a turther result ol the energization o relay 79 it opens the initial energizing cir cuit of relay 8O at armature 105, aud al armatures 102 and 104 disconnects the coin ductors 111 and 113. When conductor 112 is disconnected at armature 103, relays 12:2 and 123- ot the code switch l" and relay 8() ot the repeater E deenergize provided the wipers ot' the in'ipulse switch I happen. to be in normal position at this time. lt theyY are not in normal position, there is a ground potential upon conductor 159 associated with the wiper 160, which ground potential erztends direct to the relay 122 and through the working contact of armature and said armature to relay 1,23 and by the way of conductor 112 to the winding or relay 80 and as a result these three relays are maintained energized for Ithe time being, and the impulse switch l continues to operate and the code continues to be sent out in the usual manner until the wipers 160 and 161 reach the normal position shown in the drawings, at which time ground is removed from conductor 15S),v whereupon the three relays mentioned deenergize. Relay 122, upon deenergizing, removes ground frein conductor 165, whereupon relays 127 and 128 cease to operate.

lill

"Relay 123, upon"deenergizing, closesthe circuit of release magnet' 133 at armature 147. By the operation of release magnet 133, the shaft and wipers of the switch ld are restored to normal position in the usual manner, the circuit of release magnet 133 being opened at ,olf normal contacts 134 by the switch shaft when it reaches normal posit-ion.

ln the repeater E, relay 80, upon deenergizing in response to the removal of the Yground potential from conductor 112, removes ground from conductor 114 at armature 106, whereupon relay 126 of the switch F'deenergizes and connects up the signals S2 and S3 aga-in. As a further result of the removal of ground from conductor 112 the busy potential is removed from the release trunk conductors of all the other repeaters and any one else who desires to use the code switch may do so.

To continue with the operation of repeater E, as a result of extending the connection to back bridge relay 76 the said back bridge relayenergizes and at armat'ure `96 disconnects conductor 63 from ground and connects it to the lead ruiming Vto the ringing machine RM. Ringing ourrent is now sent out intermittently to ring the bridged bell at the substation A.

When the subscriber at substatio-n A responds by removing his receiver', a direct current bridge is closed across conductors 11 and 12 and consequently across the conductors 63 and 65 vof the repeater E, whereupon ring out oft relay 72 energizes and closes the circuit of relay 75. 4Relay 75, up- `on energizing, closes a locking circuit for `itself at armature 94, and at armature 93 places direct ground upon release trunk conductor 64 and opens the locking circuit of release relay 74. Release relay 74, however, being slow acting `does not deenergize immed-iately. As a further result of the energization of relay 75, it opens the circuit of relay 71 at armature 95. Relay 71, upon deenergizing, disconnects conductors 63 and from the ringing machine RM and ring cut oft' relay 72 respectively, and connects them to the upper and lower windings of line relay 73 again. Line relay 73, upon energizing, closes again the initial circuit 'for release relay 74 at armature 84 before the f said relay has had time to deenergize. The'calling vand called subscribers may now converse withy each other as desired, the talking circ-uitsbeing outlined by the heavy conductors.

"Referring now again to F ig. 3, it maybe `said that when it is'desired to operate the 'signa'lsfS2 and S3 without operating the sig- -nals-S and lS', a different preliminary num- 'ber is dialled with the result that a repeater `is seized which is connected with the code switch F ibyway offtheinultiple comprising conductors 111413, inclusive, andfcondu'ctor 115. lt may be said. also that when it is desired to operate both sets of signals simultaneously, a third preliminary called nu-mber is used with the resultthat a repeater* is seized which is connected with the code switch F by way of the multiple which comprises only the conductors 111-113, inclusive. Referring nowv again to the selector D, Fig. 1, the operation of the selector, in case" a subscriber attempts to establish a connection with one of the repeaters associated with the code switch while a code is being sent outwill be considered. It will be remeinbered `that while a code `is being sent*` out all the release trunk conductors associated with the calling terminals of the various repeaters are grounded. Assumingnow that the selector D is seized by a line switch such as the line switch C and that a digit /is dialled, corresponding to one of the levels in which the calling terminals of` a Vgroupof repeaters is connected, during the timefthat all the release trunk conductors are grounded, the wipers of the said selector are 'ro-7^' tated in the usual manner but not findingan idle trunk they continue to rotate until they pass off the last set of contacts, whereupon the shaft operated cam 48 operates the springs 46 and 47. Spring 46, upon being operated, opens the circuit of switching` relay 39 so as to prevent itfrom energizing at this time. Spring 47, upon being operated, connects the lead 49 with the lower winding of line relay 35 and disconnects di-" rect ground therefrom. The lead 49 extends to ground by way ofthe secondary winding of a transformer which is associated with a busy` signalling machine of any well known type such, for example, as is shown inrthe United States Patent 1,352,605, issued to Jacobsen September 14, 1920. Consequently the calling subscriber hears a busy signal to inform him that he cannot obtain the desired connection. Then the calling subscriber hears the busy signal he may replace his re;eiver thereby initiating the release of the connection in the usual manner, and call again later. rl`he operation of the selector D is the same under similar circumstances."

The various features of thcinvention, having been described and ascertained, will now be pointed out in the appendedclaims.

What is claimed is:

1. 1n a telephone system, a commonfsigf nallin-g system, two groups of terminals connected therewith and telephonical-ly connected together in pairs, one terminaliofreach pair being in one group and the other terminal in the other group, a callnuinber assigned' to one group and an answer `number assigned to the other group, automaticswitching mechanism controllable by a cal'lingsubscriber in accordance with the callgnumber `tor seizing one terminal intheg-rouptowhi-eh the call number is assigned, means responsive to said seizure for lmaking all the terminals busy except the terminal paired with the seized terminal, means controllable thereafter by the calling` subscriber in accordance with a predetermined code for operating the said signalling system to signal the called subscriber, and automatic switching mechanism controlled by the called subscriber in accordance with the answering number 'for connecting with the calling subscriber by seizin` and making busy the idle terminal.

2. n a telephone system, a common signalling system, two groups of terminals associated therewith and telephonically connected together in pairs, one terminal of each pair being in one group and the other terminal in the other group, a call number assigned to oneV group and an answer number assigned to the other group, automatic switching mechanism controllable by a calling subscriber in accordance with the call number for seizing one terminal in the group tofwhich the call number is assigned, means responsive to said seizure tor making all the terminals busy except the terminal paired with the seized terminal, means controllable thereafter by the calling subscriber in accordance with a predetermined code for operating the said signalling system to signal the called subscriber, automatic switching mechanism controllable by the called subscriber in accordance with the answering number for connecting with the calling subscriber by seizing and making busy the idle terminal, and means responsive to the last named seizure for disassociating the seized terminals from the signalling system and for making the remaining unseized terminals idle.

3. In a-telephone system, a common signalling system, a pair ot terminals associated therewith, telephone call and answer numbers assigned to said terminals, respectively, automatic switching mechanism controll-able by a calling subscriber in accordance with the call number for extending a connection to one of said terminals and for making said terminal busy when-said calling subscriber extends a connection thereto, means controlled thereafter' for operating the said signalling system in accordance with a predetermined code to signal a called subscriber, automatic switching mechanism controlled by the called subscriber in accordance with the answer number for extending a connection to the calling subscriber by seizing and making busy the other of said terminals, and means responsive to the seizure of the last named terminal for dissociating both terminals from said signalling system. f Y f 4. In a telephone system, a common signalling sytem, a plurality of groups of signals and a plurality of groups of terminals associated therewith, a separate call number assigned to each of said groups of terminals, another group of terminals equal in number to all the iirst named terminals, an answering number assigned to said last group ot' terminals, all of said terminals being telephonically connected together in pairs, one terminal of each pair being in the last meutioned group and the other terminal in one oi" the other groups, automatic switching mechanism controllable by a calling suhscriber in accordance with one oi' the call numbers for seizing one terminal in the group to which the call number is assigned, means responsive to said seizure ior making all the terminals in the several groups busy except the terminal paired with the seized terminal, means controllable thereafter by the calling subscriber in accordance with a predetermined code for operating the said signalling system to signal the called subscriber throughI the medium of one of the groups of signals, the group of signalsl used depending upon the call number used, and automatic switching mechanism controllable by the called subscriber in accordance with the answering number for connecting with the calling subscriber by seizing and making busy the idle terminal.

5. In a telephone system, a common signalling system, a plurality of groups oi signals and a plurality of groups oi terminals associated therewith, a separate call number assigned to each of said groups of terminals, another group of terminals equal in number to all of the irst named terminals, an answering number assigned to said last group of terminals, all ot said terminals being telephonically connected together in pairs, one terminal of each pair being in the last mentioned group and the other terminal. in one of the other groups, automatic switching mechanism controllable by a calling subscriber in accordance with one of the call numbers for seizing `one terminal in thc group to which that call number is assigned, means responsive to said seizure for making all the terminals in the several groups busy except the terminal paired with the seized terminal, means controllable thereafter by the calling subscriber in accordance with a predetermined code for operating the said signalling system to signal the called subscriber through the medium of one of the groups of signals, the group of signals used depending upon the call number used, and automatic switching mechanism controllable by the called subscriber in accordance with the answering number for connecting with the calling subscriber by seizing and making busy the idle terminal, and means responsive to the last named seizure for disassociating the seized terminals from the signalling system and for causing the remaining unseized terminals to test idle.

6. In a telephone system, a common signalling system, a plurality of groups of signals and a plurality o groups ot terminals associated therewith, a separate call number :ssigned to each of said groups of terminals, another group of terminals equal in number to all the rst named terminals, an answering number assigned to said last group of terminals, all of said terminals being telephonically connected together in pairs, one terminal of each pair being in the last mentioned group and t-he other terminal in one ot the other terminal groups, automatic switching mechanism controllable by a calling subscriber in accordance with one of the call numbers for seizing one terminal in the group to which that call number is assigned,` means responsive to said seizure for making all the terminals in the several groups busy except the terminal paired with the seized terminal, means controllable thereafter by the calling subscriber in accordance with a predetermined code for operating the said signalling system to signal the called subscriber through the medium of all the signals in the several groups in case a particular call number has been used, and automatic switching mechanism controllable by the called subscriber in accordance with the answering number for connecting with the calling subscriber by seizing and making busy the idle terminal.

7. In a telephone system, a common signalling system, a pair of terminals connected thereto, telephone call and answer numbers assigned to said terminals, respectively, automatic switching mechanism controllable by a calling subscriber in accordance with the call number' for extending a connection to one of said terminals and for making said terminal busy when said calling subscriber extends a connection thereto, means controllable thereafter by the calling subscriber for operating said signalling system in accordance with a predetermined code to signal a called subscriber, automatic switching mechanism controllable by the called subscriber in accordance with the answering number for connecting with the calling subscriber by seizing and making busy the other terminal, and means responsive thereto in case the calling subscriber' has replaced his receiver for signalling the calling subscriber.

8. In a telephone system, subscribers lines, a common signalling device accessible to said lines, automatic switching devices controlled by a calling subscriber for extending a connection to said device, for operating the same to signal any subscriber and for rendering the device busy to other subscribers, and other automatic switches controlled by the subscriber called for completing a connection with the calling subscriber and for again rendering said device idle responsive to said connection'being completed.

9. In a telephone system, subscribers lines, a line accessible in common to all of said subscribers lines, signal controlling apparatus associated with said line, means for seizing said last line and for making it busy when seized, means including said apparatus and operable thereafter for signalling called subscriber by means of a signal associated with said last line, means whereby the subscriber signalled may telephonically connect with the calling subscriber, and means responsive thereto for freeing the last mentioned line and for permitting said apparatus to be again used to signal the called subscriber.

In witness whereof, I hereunto subscribe my name this 19th day o'l' Oct., A. D. 1921.

,WILLIAM A. CI-IAPIN. 

